From the beginning, espresso beverages have been prepared by passing a measured amount of hot water through a filter which carries a quantity of ground espresso beans. Upon passing through the filter, the water picks up bean particles, transforming the water into "espresso" for consumption, either alone, or as an ingredient of a further-prepared beverage or drink. The final product may, for example, take the form of a "cappuccino", a beverage which includes both espresso and a quantity of hot frothed milk. Such beverages may of coarse be prepared manually, but more often arc prepared using a somewhat automated espresso machine.
In a conventional espresso machine, espresso is prepared using a pressurized boiler which provides hot water for injection through the ground espresso beans and into a prepositioned cup. The boiler also provides high-pressure steam for passage through a steam discharge nozzle, the nozzle being configured to extend into a container of milk to simultaneously heat and froth the milk. In order to promote the admission of air into the milk, the container is slowly moved up and down relative to the nozzle, thus enhancing the frothing process. The hot frothed milk then is added to the espresso, is garnished, and is served to the consumer as a "cappuccino".
Although relatively simple, the above-described arrangement is inadequate in several respects. For example, those skilled will appreciate that pressurized boilers are expensive to manufacture, generally requiring construction of a material such as copper or brass. Further, the use of a boiler may be dangerous to the operator, particularly in the event of boiler failure, an event which may result in uncontrolled discharge of hot water or steam. Such a failure similarly could damage surrounding property, and could injure others in the vicinity of the machine. It thus would be desirable to provide an espresso machine which does not require the use of a pressurized boiler.
The aforementioned milk frothing system also is less than optimal, the system's operation requiring more than a minimum degree of expertise. Namely conventional milk frothing requires proper positioning of the nozzle within the milk container, and :requires a proper frequency and amplitude of up and down container movements. In addition, the use of steam to heat and froth milk can result in operator injury due to splattering of hot milk. For example, if the container holds a relatively small "quantity" of milk and the nozzle is positioned at a level where steam can escape above the upper level of milk, droplets of milk could be sprayed from the container to the area surrounding the espresso machine.
What is needed is an espresso machine which is capable of simply and safely providing hot frothed milk. More particularly, it would be desirable to provide a milk heating and frothing system which does not require the use of a boiler, and which does not require the use of steam.